Retrieval analysis offers a direct insight into in vivo wear mechanisms. However, the 3D measurement of wear patch characteristics on spherical highly reflective bearings has been difficult. An instrument based on an optical technique has been developed over the past 3 years. It is capable of scanning metallic head and cup in a single measurement, within minutes, at a resolution of 20 nm. From the cloud of 3D points obtained during scanning (typically 35,000 To 1,000,000), a 3D image of the measured part can be obtained. The associated computer program allows for sphericity, roughness, radius and local radius to be calculated, and surface maps of the 3D model can easily be plotted.

Both head and cup of two failed MoM resurfacing devices, a wear simulator test couple and intact components were analysed using the new technique. A successful McKee Farrar head (20 years in vivo) was also scanned. Results were compared with traces obtained on a Mitutoyo RA 300 roundness machine (resolution 0.01 microns).

3D maps of the bearing surfaces of MoM devices were obtained. The maximum linear wear values on heads were 2.5 microns, 99 microns 53.5 microns and 298 microns for the simulator sample, the McKee Farrar head and the two failed resurfacing devices respectively. The corresponding maximum linear wear values on cups were 11 microns, 529 microns and 645 microns for the simulator sample and the two failed resurfacing devices respectively. These results were in good agreement with results obtained on the Mitutoyo machine. Contrary to other worn samples, the two latter cups showed that the cup had worn on the edge of the bearing surface. This resulted in an oval shaped wear patch on the head. For the McKee Farrar device and the simulator device, the wear patch was away from the edge and the outline of the wear patch was circular in shape.

This novel technique has allowed for high resolution 3D mapping of the full bearing surfaces on successful McKee Farrar device and on more recent resurfacing devices. Further studies are required. However, the results suggest that component positioning is paramount to wear performance of metal on metal devices.

Aim: Lower friction in metal on metal (MOM) hip joints can reduce the wear, production of metal ions and loosening of acetabular cups. The effect of the fluid viscosity on the friction, especially in the relation to the physiological range, is still not fully investigated. The aim of this paper was to study the frictional behaviour of MOM hip joint within the human physiological fluid viscosities.

Materials and Methods: Friction measurement was carried out using a friction simulator on CoCrMo hip prostheses of 50 mm diameter with 100 and 200 micron diametral clearances. The samples were taken from a wear simulator test at 1.4, 2.3 and 3.2 million cycles. A dynamic loading of 100–2000N was applied to the femoral head with a movement of 1 Hz and +/−23 degree amplitude. Tests were performed using 25% new born calf serum which consisted of different ratios of serum and carboxymethyl cellulose with viscosities ranged from 0.0011 to 1.1 Pa s determined by a viscometer at a shear rate of 300/s.

Results: The friction of both clearances reduced with the progress of wear. In the lower range of viscosity, the friction of 100 micron clearance was lower than that of 200 micron clearance. However, when the viscosity reached the range of 0.01–0.06 Pa s, the friction of 100 micron clearance surpassed that of 200 micron clearance and this difference became wider with the increase of viscosity. During one measurement, the curves of 100 micron clearance started from low friction (≈0.05), but increased rapidly for all viscosities except the lowest of 0.001 Pa s. For the 200 micron clearance, the curves were stabilized when the viscosity was below 0.36 Pa s and low friction was observed as the viscosity increased. The friction started to increase only from 0.36 Pa s, but the gradient was less stiff compared to that of 100 micron clearance.

Discussion: Normal synovial fluid is non-Newtonian in nature with shear-rate dependent viscosity. Researchers have reported 300/s shear rate viscosities for normal, osteoarthritis, and inflammatory synovial fluids as 0.010.4, 0.0025–0.2 and 0.001–0.07 Pa s respectively. In this study, the 200 micron clearance had lower friction than that of 100 micron clearance in the majority of physiological viscosity range. Theoretical studies have suggested that smaller clearance and higher viscosity can benefit the lubrication in MOM bearings. However, this theory is valid if continuous and complete lubrication film is achieved. Small clearance and high viscosity may prevent the recovery of lubricant between cycles and cause depletion of lubricant, which can lead to direct contact of bearings and increase of friction. It is therefore concluded that the selection of clearance for MOM components should consider the human physiological fluid viscosities so that an optimal tribological performance can be achieved.

Acetabular cup orientation in hip arthroplasty is critical to prevent edge loading and impingement. Aerial alignment guides position the cup at a specified angle to the orthogonal planes, but only if the pelvis is in strict lateral-decubitus. Computer navigation can also be used to position the acetabular cup, but there are limitations associated with defining the pelvic reference plane. It can also be postulated that a fixed angle of inclination and anteversion is not suitable for every patient and every cup design. This paper describes the development and testing of instrumentation that allows patient specific acetabular cup placement without knowing the exact pelvic orientation.

Stage 1 determines the cup position during a trial reduction. A Judd nail retractor is left in the pelvis during the trial reduction. A single-use laser pointer is attached to the top of this nail, is free to move and can be locked in position. The trial acetabular cup has a handle protruding at a fixed angle from the face of the cup. At the end of this handle is another single-use laser pointer that projects a laser beam parallel to the axis of the cup onto the wall/ceiling. Keeping the handle parallel to the medio-lateral axis to control inclination angle, the leg is moved through a range of motion (ROM). The anteversion of the trial cup is adjusted until a position is found where flexion extension ROM is possible without impingement and satisfactory abduction-adduction is achieved with stability. Once this position is found, the Judd nail laser (fixed to the pelvis) is adjusted until its projected point, on the wall/ceiling, coincides with that from the trial handle. The Judd nail laser is then fixed in position, the hip dislocated and trial components removed.

Stage 2 aligns the definitive acetabular cup. The introducer has a laser pointer pointing parallel to its axis (away from the patient) and is attached to the definitive cup. The definitive cup is placed in the acetabulum and the introducer adjusted until its projected laser coincides with that from the Judd nail. The cup is then in the same orientation as determined during the trial reduction and can be impacted.

To demonstrate the accuracy of the laser alignment method, the position of the definitive cup was compared to that of the trial cup in polyurethane foam models. With the laser points projected onto an object > 2m away, the accuracy was ±2°.

To compare the laser guided instrumentation with the conventional aerial device, the ROM of the definitive cup was assessed in Sawbones resurfaced pelvis/femur models. The pelvis orientation was rotated by ±10° about the medio-lateral axis and the superio-inferior axis to investigate the effect of the pelvis being unknowingly out of lateral-decubitus. In the worst case of pelvis position, the aerial halved the required flexion and allowed double the required extension. The laser guided instrumentation maintained the physiological range of flexion/extension regardless of pelvis position and is therefore considered an improvement on current technology and a viable alternative to computer navigation.

Charcot arthropathy is a non-infective destructive process manifesting as dislocation, periarticular fracture or a combination of both, in patients with peripheral neuropathy

The classification and staging of charcot arthropathy assists us in decision making and appropriate management of these patients. Clinical presentation and diagnosis will be discussed as well as management techniques for the different stages of arthropathy. Neuropathic ulcer management, including new ideas, will be briefly covered.

Variability in femoral head preparation and high cement pressures may be associated with failure to seat femoral components during hip resurfacing. Furthermore, excessive pressures may lead to over penetration of bone by cement with resulting necrosis of the underlying bone. We designed an experimental model to test the hypothesis that partial-length pressure-relief slots made longitudinally in the proximal bone of the femoral head, without extending to the head neck junction, would allow controlled leakage of cement during initial insertion of a femoral head resurfacing component, but would then become sealed during final insertion to prevent excessive loss of cement while still allowing accurate seating of the component.

Thirty-one resurfacing femoral components were cemented onto foam femoral head models. The clearance between foam model and implant was measured to determine the minimum space available for cement. Eleven components were inserted using hand pressure alone, 20 were hammered. Pressure relief slots were prepared in 10 femoral heads. The slots, 4mm deep grooves, were made in the proximal bone only, without extending to the head-neck junction. Cement pressure inside the component was measured during insertion. Implants were sectioned after implantation in order to determine whether they had been fully seated or not. The clinical relevance of the measures taken was tested by measuring the diameter of prepared femoral heads during 20 hip resurfacing operations in order to determine the extent of variability in intra-operative femoral head preparation.

Mean intraoperative clearance between bone and implant was −0.19mm (0.11 to −0.93mm). Mean clearance between foam model and implant was −0.30mm (0.35 to −0.94mm). Full seating was obtained in 22/31 components. Of those not fully seated, all had clearance less than −0.74mm. Full seating with a clearance of less than −0.35mm was only possible when pressure relief slots had been made in the femur. The use of a pressure relief slot longer than half the femoral head length allowed full seating in 9/9 cases, compared to 13/22 without. Cement pressure obtained with a hand pressure technique was less than half that observed with hammering (20.8vs56.0psi, p=0.0009) but was not associated with failure to seat the implant if a slot was used.

Variability of the actual diameter of the femoral head prepared may be associated with difficulty in fully seating resurfacing components. The same degree of variability in the space available for cement was observed in both intra-operative and test specimens. The use of a pressure-relief slot allows full seating of resurfacing implants with hand pressure alone, thereby halving cement pressure, in an experimental model, even when clearance between implant and bone is less than optimal.

The clearance between the femoral head and the acetabular cup can significantly affect the lubrication, the wear and the lifetime of metal on metal (MOM) hip joints. The objective of this study was to compare the frictional behaviour of MOM joints with different clearance.

Two CoCrMo MOM 50mm diameter hip joints, with a small diametral clearance of 17 microns and a big diametral clearance of 212 microns, were used in this study. The friction measurement was carried on the wear patches of MOM bearings during a long-term wear simulator test. A dynamic trapezoidal-form loading cycle was applied to the femoral head with a minimum load of 100N during the swing phase and a maximum load of 2000N throughout the stance phase. A simple harmonic motion of amplitude +/−24 degree was applied to the femoral head in the flexion-extension plane with a frequency of 1 Hz. The friction torque was measured at 0, 0.8, 1.3, 1.9, 4 and 5.5 million cycles using 6 different viscosities of 25% new born calf serum.

The results show that the friction factors (f) of small clearance were generally higher than those of big clearance and this difference became wider with the progress of wear. The lower f of big clearance, especially in the lower range of Sommerfeld number (z) after 5.5 million cycles, is significant and will affect the ultimate performance of prostheses as this range has closer rheological properties to synovial fluid and represents long term wear conditions. At the same time, the friction factors were always higher every time when measured from high z to low z, although this difference became slightly smaller with the progress of wear, which indicates that there is still direct contact between the bearings. The lower friction factor when increasing z, is due to the wear and bedding-in with the progress of the measurement. It is concluded that large clearance has lower friction factor than small clearance, and full fluid film lubrication is unlikely to have developed between the MOM bearings in this study, even with a small clearance and high viscosity.

We previously compared the component alignment in total knee replacement using a computer-navigated technique with a conventional jig-based method. We randomly allocated 71 patients to undergo either computer-navigated or conventional replacement. An improved alignment was seen in the computer-navigated group.

The patients were then followed up post-operatively for two years, using the Knee Society score, the Short Form-36 health survey, the Western Ontario and McMaster Universities osteoarthritis index, the Bartlett Patellar pain questionnaire and the Oxford knee score, to assess functional outcome.

At two years post-operatively 60 patients were available for assessment, 30 in each group and 62 patients completed a postal survey. No patient in either group had undergone revision. All variables were analysed for differences between the groups either by Student’s t-test or the Mann-Whitney U test. Differences between the two groups did not reach significance for any of the outcome measures at any time point. At two years postoperatively, the frequency of mild to severe anterior pain was not significantly different (p = 0.818), varying between 44% (14) for the computer-navigated group, and 47% (14) for the conventionally-replaced group. The Bartlett Patellar score and the Oxford knee score were also not significantly different (t-test p = 0.161 and p = 0.607, respectively).

The clinical outcome of the patients with a computer-navigated knee replacement appears to be no different to that of a more conventional jig-based technique at two years post-operatively, despite the better alignment achieved with computer-navigated surgery.

The use of navigation systems to aid in the performance of total knee replacement has become an accepted method of treatment. Previous studies have shown that by using computer aided navigation the components can be implanted with more reproducible accuracy.

We present the results of a prospective randomised trial, with ethical committee approval that was performed to compare the use of a new, two-pin system with the original three-pin system to fix the tracker to bone. There were 37 patients in the two-pin group and 31 patients in the three-pin group. Pre-operative demographic data was similar. Patients were assessed pre and post operatively clinically using the Knee Society Score, WOMAC and SF36. Radiographic assessment was performed using “The Perth CT Protocol.”

At one year there was no significant difference clinically between either group. Radiographic assessment showed no significant difference in the results of all the prosthesis variables as measured by the Perth CT Protocol, except in the femoral prosthesis absolute varus/ valgus position, with the two-pin group being more accurate. The upgraded tracker fixing system in the computer navigation system allows as accurate implantation as the earlier system with less patient morbidity.

During conventional hip arthroplasties, the diseased femur is rigidified using a metallic stem. The insertion of the stem induces a change in the stress distribution in the surrounding femur, and the bone remodels; this stress distribution is a direct result of the stem stiffness characteristics. Healthy healing of the femur requires that the bone be loaded as naturally as possible. If the bone is not loaded appropriately, it can resorb which may result in stem loosening and revision. Although current rigid metallic femoral stems are very successful, a poor stress distribution may become a critical problem for younger patients as the stem/femoral bone construct will be subjected to higher loads for longer times, and since remodelling is faster, loosening can occur earlier. Reduced stiffness stems have therefore been investigated, but early failures have been reported due to increased movements, poor initial stability and the low proximal stiffness of the stem. A novel biocompatible carbon fibre reinforced plastic (CFRP) stem has been developed in light of these past experiences1. Using a series of analytical models and experimental validation tests1, the fibre type and architecture have been tailored along and across the stem to achieve healthy bone remodelling and proximal strength of the construct. In addition, a biocompatible hydroxyapatite coating was specifically designed to enhance interface strength and stability2. The present study describes the mechanical behaviour of this novel stem with particular emphasis on the stem/bone interface. 4 static and 29 fatigue tests were performed according to ISO7206; these tests were complemented by acoustic emission monitoring to identify failure mechanisms3. A stress versus number of cycles to failure (SN) curve was obtained to describe the fatigue behaviour (i) under constant amplitude cycling at various load levels and (ii) incorporating rest periods and overloads. In addition, a mechanical test was designed to characterise the motions between the bone and the stem during sinusoidal fatigue loading (5000 cycles, 0.2–2kN, 1Hz). Two linear variable differential transformers measured the vertical and horizontal displacements at the stem/ bone interface in the proximal region. 3 tests were performed on CFRP stems and 3 on a metallic stem. The CFRP stem exceeded the standard requirements. The SN curve showed good repeatability across the loading spectrum. The inclusion of overloads/static loads during fatigue had a beneficial effect on the stem endurance. This is attributed to the development of microcracks, which dissipate the load, and to creep of the resin. The amplitude of recoverable motion observed at the interface during each load cycle was similar for both types of stem (20mm and 4mm in the horizontal and vertical directions respectively) and remained below the recommended limit4. Composite materials offer high design flexibility. This has been exploited in the development of a compliant, mechanically tailored biocompatible hip stem for femoral reconstruction, and could provide an answer to hip replacement for younger, more active patients.

The concept of a congruent and incongruent joint will be introduced and the results of various distal osteotomies will be presented. The differential diagnosis of pain around the 1st metatarsophalangeal joint will also be discussed.

Although not exclusively a complication of distal osteotomies, the correction of acquired hallux varus will also be presented.

We investigated the blood supply of the common peroneal nerve. Dissection of 19 lower limbs, including six with intra-vascular injection of latex, allowed gross and microscopic measurements to be made of the blood supply of the common peroneal nerve in the popliteal fossa. This showed that a long segment of the nerve in the vicinity of the fibular neck contained only a few intraneural vessels of fine calibre. By contrast, the tibial nerve received an abundant supply from a constant series of vessels arising directly from the popliteal and posterior tibial arteries.

The susceptibility of the common peroneal nerve to injury from a variety of causes and its lack of response to operative treatment may be explained by the tenuous nature of its intrinsic blood supply.

Aim

To determine the prevalence and distribution of pain in patients with Charcot-Marie-Tooth disease and the effects of surgery on this pain.

Methods

Members of the Charcot -Marie -Tooth International support group were sent a pain questionnaire. Data about the site, nature, frequency, severity of pain, pain triggers, methods of pain relief and the response to surgery were collected.

Results

There were 399 respondents (233 women and 166 men). The most frequently reported sites of pain were the legs (79%) and feet (77%). Ankle pain was reported by 57%. Walking and exercise were the most frequent pain triggers. Rest was the most common method of modifying pain (60 % of respondents). 32 % found analgesics effective and 39% used heat to relive their pain. The most common sites for surgery were the foot (36%) and ankle (26%). In 43% of patients undergoing foot surgery and 54% of patients undergoing ankle surgery, pain had been increased or introduced following surgery.

Conclusions

Patients with Charcot-Marie-Tooth disease experience significant inherent, and probably neuropathic, pain in addition to pain from mechanical causes. Surgery is unlikely to improve or eliminate pain in these patients. It may introduce pain in some. Surgery should be confined to the treatment of structural problems, as it is often ineffective at relieving pain.

We report the results of seventy-six Harris Galante Porous Cups (HGP 1) in sixty-three patients treated by Total Hip Arthroplasty (THA) with a diagnosis of avascular necrosis (AVN) of the femur (grade III and IV). The cups were inserted between 1986 and 1994 and followed prospectively. Seventy hips with a follow up of more than five years (mean 7.6 years) were reviewed.

At last review the mean Harris Hip Score was 94 (standard deviation (& dcl001;) .8), preoperatively the mean had been 29 (& dcl001;14.7). Radiographically there was no evidence of acetabular migration. The revision rate of the femoral prosthesis was 8.6%, however only three stems (4.3%) were revised for loosening the rest being revised to allow down sizing of the femoral head. The revision rate for the acetabular prosthesis was 7.1%, (five cups). At the time of revision none of the cups were clinically loose and only required the liner to be changed. The complication rate was low with no deep infections or dislocations and only nine hips, (11.8%) with grade III heterotopic ossification. Survival analysis for both stem and cup at 8 years is 96.3% (confidence interval 91 – 100%), with a worst-case survival of 93.6%, (C.I 87.4 – 99.9%)

Previous studies of patients undergoing cemented THA for the treatment of advanced AVN have reported a high incidence of component loosening. This study shows good medium term results using the Harris Galante Porous cup for acetabular reconstruction with cemented femoral components for the treatment of this difficult problem.

This study assesses the clinical performance of the Souter-Strathclyde elbow arthroplasty with a standardised index and long term survivorship analysis.

We undertook assessment of 68 primary Souter-Strathclyde total elbow replacements. Of 53 patients assessed with pre-operative Souter-Strathclyde charts, nine died and one was lost to follow-up, 43 had radiographic and telephone review, and 38 (88%) had clinical examination according to the Mayo Elbow Performance Index.

Survival of the 43 elbows was to a mean of 72 months (range: eight to 187 months) with improvement in pain, motion, stability and function. Eight of 10 elbows in deceased patients had satisfactory scores at the last assessment. Ulnar neuropraxia occurred in eight elbows (12%), persistent sensory deficit in two (3%) and motor deficit in one. Two triceps abscesses required local skin flap cover. Revision was undertaken in 14 elbows (20%) for instability (six) bony injury (three), loosening (three) and intraoperative problems (two).

The survivorship at 13 years was 74% with 62 (91%) of all elbows achieving a satisfactory Mayo score.

The production of particulate wear debris is a recognised complication of joint arthroplasty, but interest has concentrated on local tissue reactions and a possible association with implant loosening. The fate of wear products in the body remains unknown, although some of the metals used in the construction of orthopaedic implants are known to have toxic and oncogenic properties. We report histological and electron-microscopic evidence from two cases which shows that metallic debris can be identified in the lymphoreticular tissues of the body distant from the hip some years after joint replacement. The increase in the use of total arthroplasty in younger patients, the development of new alloys and the use of porous coatings must raise concern for the long-term effects of the accumulation of wear debris in the body.

In fifty-six patients with ankylosing spondylitis three types of arthroplasty had been performed in ninety-nine hips. Forty-one of the patients were men and fifteen were women, their average age at operation being forty-two years. Primary pseudarthrosis produced well-satisfied patients, but only a fair result in five hips, whereas cup arthroplasty resulted in a poor outcome for eight hips, all of which needed revision. Total replacement of eighty-six hips, however, led to 73 per cent being graded as good or excellent up to ten years later. The main complications were deep infection of five hips, para-articular ossification around nine hips (six leading to bony ankylosis), and fibrous ankylosis of six hips.

The results of excision of the head of the radius in forty-four elbows affected by rheumatoid arthritis are presented. Relief of pain was obtained in 90 per cent and an increase in the range of flexion and extension was seen in 70 per cent. Involvement of the humero-ulnar joint seen radiologically is no contra-indication to the operation; simple excision of the radial head often gives gratifying results; In our experience the relief of pain and increased range of movement have greatly reduced the need for total replacement arthroplasty.